It has long been recognized that the application of heat to muscles or joints which have been strained or injured or which suffer from certain ailments is highly beneficial and comforting. Sports related strains or injuries, in either human or other animal participants, have received particular attention. While the application of cold packs is often used immediately following an injury for an interval of some hours, subsequent treatment is often by applying heat.
It is, however, difficult to apply heat to an injured limb or other body part without severely restricting mobility of the patient. Various techniques have been and are used to provide heat, or the sensation thereof, in a portable fashion to permit mobility, including packs of heated fabrics and various rubefacients. However, their effects tend to be of very short duration since normal heat loss cools the hot packs quickly unless they are of burdensome volume and weight, and rubefacients tend to be either too strong at the outset or to have little effect after a brief interval.
Another approach which has been taken is the provision of a heating element enclosed within a fabric pad, or layers of pads, the element being heated by electrical current. The element and pad assembly is attached to a belt, band or strap arrangement having fasteners of conventional type so that it can be worn by the patient with the heating element adjacent the body area needing treatment. In order to make such a device portable, the current is supplied by a chemical battery, usually of the dry cell type, disposed in a pocket or otherwise carried on the body.
Recent advances in the power-delivering capabilities of batteries have made such devices more practical than before, but it remains true that these physically small power supplies have limited current-supplying capabilities over a limited interval of time, i.e., the current-time product is relatively small. Thus, prior art efforts to produce an efficient and effective portable therapeutic heating pad have not met with significant acceptance. Examples of prior art efforts in this general area are found in the following documents:
U.S. Pat. No. 2,178,397--Larkey PA1 U.S. Pat. No. 3,016,446--Kalbach PA1 U.S. Pat. No 3,178,559--Fogel et al PA1 U.S. Pat. No. 3,292,628--Maxwell et al PA1 U.S. Pat. No. 3,470,350--Lewis PA1 U.S. Pat. No. 3,569,666--Murphy et al PA1 Norwegian Pat. No. 109,776--Krosby